Symptoms may occur as soon as three days or as long as two months after infection. The typical incubation period is thought to be one to three weeks.

Foods typically linked to listeriosis are deli meats, hot dogs, and soft cheeses made with unpasteurized milk. Produce is less often linked to outbreaks, although listeria is found in soil and water. Listeria is killed by cooking, but it can grow and multiply in refrigerators.

How to Avoid Listeria

The CDC has issued this advice:

People at high risk for listeriosis, including older adults, people with weakened immune systems, and pregnant women, should not eat cantaloupes marketed as coming from the Rocky Ford region of Colorado.

People who have cantaloupes in their homes can check the label or inquire at the store where they purchased it to determine if the fruit was marketed as coming from the Rocky Ford region of Colorado.

Listeriosis primarily affects older adults, people with weakened immune systems, pregnant women, and newborns. People who think they might have become ill from eating possibly contaminated cantaloupes should consult their doctor immediately.

Cantaloupes marketed as coming from the Rocky Ford region should be disposed of in a closed plastic bag placed in a sealed trash can. This will prevent people or animals from eating them.

As other foods besides cantaloupes can carry listeria, the CDC recommends these general steps to avoid listeriosis:

Rinse raw produce, such as fruits and vegetables, thoroughly under running tap water before eating. Dry the produce with a clean cloth or paper towel before cutting them up.

Thoroughly cook raw meat and poultry.

Heat hot dogs, deli meats, and cold cuts until they are steaming hot just before serving.

Do not drink raw (unpasteurized) milk and do not eat fresh soft cheeses that have unpasteurized milk in them, especially Mexican-style cheeses like queso fresco.

Be sure that your refrigerator is at or below 40 degrees F and your freezer is at or below 0 degrees F by using a refrigerator thermometer.